The present invention relates to the general field of devices for adjusting a fluid flow rate, and more particularly to that of devices for adjusting the feed rate of fuel injectors provided for the combustion chambers of turbomachines.
In conventional manner, a turbomachine engine has a plurality of injectors enabling the combustion chamber to be fed with fuel and air when starting and during normal operation of the turbomachine engine. There exist two main types of injector: “aeromechanical” injectors designed for two fuel flow rates (a primary rate and a secondary rate) depending on the operating stage of the engine (lighting, or from low to full power), and “aerodynamic” injectors which have only one fuel circuit for all stages of operation. The present invention relates more particularly to injectors belonging to the second category.
In conventional manner, a fuel injector for a turbomachine engine comprises in particular a metering valve arranged to open under a predetermined fuel feed pressure and to remain open in response to an increase in said feed pressure so as to enable fuel to be admitted and then ejected towards the nose of the injector where the fuel is sprayed into the combustion chamber. The fuel feed rate is adjusted by means of metering slots provided in a head of the valve and presenting flow sections that vary as a function of the applied feed pressure: the higher the feed pressure, the greater the flow sections of the slots.
In practice, it is found that in a combustion chamber fed with fuel and air by a plurality of injectors of the kind described above, there exist differences in flow rate on opening and/or closing the respective valves even when said injectors are all subjected to the same feed pressure. These flow rate differences between injectors are caused by a hysteresis phenomenon due to friction between the injector valve and the bushing in which it slides. Thus, two identical injectors subjected to the same feed pressure can present different flow sections via their metering slots. This causes the feed of fuel into the combustion chamber to be non-uniform by an amount that can be as great as 45%, and this in turn can lead to difficulties in lighting the turbomachine engine, and can even prevent the engine from lighting.